Diffusion tensor imaging of the visual pathway in dogs with primary angle-closure glaucoma

Area of Science:

• Veterinary ophthalmology
• Neuroimaging
• Canine vision research

Background:

• Primary angle-closure glaucoma (PACG) is a significant cause of vision loss in dogs.
• Understanding structural changes in the visual pathway beyond the optic nerve head is crucial for diagnosing and managing canine PACG.
• Current imaging techniques may not fully capture subtle, in vivo alterations in the visual pathway.

Purpose of the Study:

• To quantify in vivo structural integrity of the canine visual pathway (optic nerve, chiasm, tract, LGN) using diffusion tensor imaging (DTI).
• To compare DTI metrics between dogs with and without PACG.
• To establish the reliability of DTI measurements in canine visual pathway structures.

Main Methods:

• A prospective pilot study utilized 3-Tesla DTI on six dogs with PACG and five matched controls.
• Quantitative DTI indices (e.g., fractional anisotropy, radial diffusivity) were measured in the optic nerve, optic chiasm, optic tracts, and lateral geniculate nucleus (LGN).
• Comparisons were made between normal, unilateral PACG, and bilateral PACG groups; intra-observer reliability was assessed using the intra-class correlation coefficient (ICC).

Main Results:

• DTI successfully provided quantitative measurements for all assessed visual pathway structures in all dogs.
• A trend of reduced fractional anisotropy (FA) was observed in structures associated with PACG.
• Dogs with unilateral PACG showed consistently higher FA and radial diffusivity (RD) in the optic nerve of the unaffected eye compared to normal dogs.

Conclusions:

• DTI provides a reliable and quantifiable method for evaluating the canine visual pathway in vivo.
• DTI metrics like diffusivity and anisotropy hold potential for detecting axonal injury and transsynaptic degeneration in canine PACG.
• This neuroimaging approach may offer novel insights into the pathogenesis and progression of canine glaucoma.